1. Field of the Invention
This invention relates to a piezoelectric resonator utilizing the longitudinal vibration mode and to a construction for a piezoelectric resonance part having said piezoelectric resonator packaged therein.
2. Description of the Prior Art
Heretofore, in a frequency region of 200-800 KHz, a piezoelectric resonator in the form of a quadrangular or circular plate utilizing expansive vibration has been used. The size of the piezoelectric resonators differs with intended frequency. The length l of one side of a quadrangular one and the radius R of a circular one are determined by dividing a: frequency constant by the intended frequency. The thickness t of the element is fixed so that 0.03l(R)&lt;t&lt;0.2l(R). The use in the range of 200-800 KHz is due largely to problems of economics and of processing accuracy.
FIG. 1 is a sectional view showing an example of a conventional piezoelectric resonance part having this type of piezoelectric resonator housed therein. Opposite surfaces of a piezoelectric ceramic 1 are formed with electrodes 2 and 3, forming a piezoelectric resonator. Spring terminals 4 and 5 are connected to the middle portions of the electrodes 2 and 3 of this piezoelectric resonator where the vibratory displacement is relatively small, said spring terminals 4 and 5 being led out of a case 6. In addition, reference numeral 7 denotes a sealing resin.
It has been pointed out that the aforesaid conventional piezoelectric resonator and piezoelectric resonance part present various problems to be described below.
In a frequency region close to 200 KHz, the aforesaid length l or radius R becomes about 11 mm, a value which means a considerably large-sized and expensive article. Moreover, since the electrodes 2 and 3 make point contact with the terminals 4 and 5, even a slight shock can cause damage thereto.
On the other hand, in a frequency region close to 800 KHz, the length l or radius R is about 2.5 mm, which means a very small size, but this small size results in the points of contact of the metal terminals 4 and 5 with the electrodes 2 and 3 deviating from the middle where the vibratory displacement of the resonator is small, thus presenting a problem that a variation in electric characteristics is liable to occur.
Further, in the package construction of the conventional piezoelectric resonance part shown in FIG. 1, the entire configuration is large and the size of the resonator varies considerably with intended frequency, so that uniformity of the shape of cases cannot be attained; thus, cases of various sizes and shapes are required. Similarly, since the base board size of the resonator changes with intended frequency, not only the cases but also other parts such as terminals must be designed and manufactured individually according to intended frequencies. Further, the leads to be led out of the case must be prepared in various pitches, lacking in interchangeability and making it difficult to reduce cost. Further, the construction of FIG. 1, which is employed to enable the resonator to vibrate freely in the case, requires a relatively large number of assembling steps, leading to a reduction in efficiency of production.